There are many situations where it is desired to remove, reduce the amount of, or prevent the formation of contaminants such as water, ice, particulate, and other substances from windows or other surfaces. Recent solicitations have sought improved ways to keep submarine periscope windows dry and clean, ways to keep clean the mirrors and windows of high power lasers, and ways to clean the surfaces of the “last optic” in future laser fusion reactors. Photographs and TV pictures are also sometimes seriously degraded by the water drops on the protective window in front of the camera. Forward looking infrared (FLIR) systems also benefit from clean and dry windows. In addition, the push to high yields of smaller and smaller circuit features in the semiconductor industry has made contamination removal from semiconductor surfaces a high priority.
A great deal of research and development has been published on the use of lasers to remove contaminants, such as particles and films, from the surfaces of solid materials. All of this prior work illuminated the contaminated surface from the outside of the surface, usually from the side that is exposed to vacuum or air.